The NILE-related glycoproteins are a family of 215-230 KD molecules found on neuronal cell surfaces. A given nerve cell type expresses a specific form of NILE which differs from other NILE molecules at both the polypeptide and oligosaccharide levels. In vitro experiments show that anti-NILE antibodies can interfere with the formation of fiber bundles, suggesting a role for NILE in neurite fasciculation. In keeping with this immunofluorescence experiments show that during the development of the rat nervous system NILE appears on axons at the time of formation of nerve fiber tracts. Future research is aimed at achieving a more detailed understanding of the structure, distribution, and function of the NILE-related glycoproteins. Since both NILE and N-CAM appear to be involved in neurite fasciculation, it is important to establish when NILE appears in nerve fiber tracts relative to N-CAM and whether the distribution of the two molecules in fiber tracts is similar. This can be determined by immunohistochemical mapping with anti-NILE and anti-N-CAM. The molecular forms of NILE present in different parts of the developing nervous system will be analyzed by immunoblotting. This will help corroborate in vitro data which shows the existence of multiple forms of NILE, and will indicate whether or not NILE, like N-CAM, undergoes a maturation process during progressive stages of fiber tract development. The mechanisms controlling NILE expression during neuronal differentiation will be investigated using a clonal cell line, EC1003. These embryonal carcinoma cells can be induced by serum deprivation to differentiate from a NILE-negative, neuroepithelial state to a NILE-positive, neurite-bearing state. The role of NILE in mediating fiber bundle formation will be investigated in vitro with a series of primary culture systems designed to test the relative effectiveness of anit-NILE and anti-N-CAM in disrupting neurite fasciculation. The disruptive effects of anti-NILE on the development of nerve fiber tracts will be tested in vivo by transplacental administration of antibody to rat fetuses. For studies at the molecular level, the ability of immobilized NILE to promote the adhesion of cells and of latex beads coated with a variety of cell surface and extracellular matrix molecules will be assayed quantitatively. In this way, the molecular interactions responsible for NILE-mediated adhesions between neurites can be identified.